The primary targets of HIV-1 are monocytes/macrophages of various lineages and T-lymphocytes of the immune system. As virological and immunological in vitro assays are greatly influenced by the composition of the viral stock such as soluble viral glycoprotein, defective interfering particles and half life of viral particles, we therefore compared the growth rates, titers, and physico-chemical properties of an HIV-1 Ada, an uncloned isolate obtained from and maintained in peripheral blood macrophages, and a T-cell line-adapted strain HIV-1 MN. The studies were performed using peripheral blood mononuclear cells (PBMC) and macrophages derived from a single donor by monitoring viral proteins and enumeration of virions with electron microscopy (EM). For HIV-1 Ada grown in macrophage, the number of the virions obtained by EM was about 3.2 x 10(9)/ml agreeable to that calculated from the p24 concentrations (250 ng/ml = 5 x 10(9) virions), and is estimated to be 10(9) virions/day produced by 10(7) cells. The numbers of gp120 molecules as estimated from p24 concentration were in the range of 1 to 2 x 10(2)/virion. This is 10 to 20 times more gp120/virion than was observed in a T-cell line-adapted laboratory strain of HIV-1. The majority of p24, RT, and gp120 was found to be associated with virions pelleted by ultracentrifugation, indicating minimal shedding of gp120 molecules. Titration of clarified HIV-I Ada had similar physico-chemical properties regardless of their host cell of origin, and were titered in the range of 10(3) to 10(5) infectious units/ml. These findings now allow for more accurate and detailed in vitro immunological and virological studies to be performed in the development of intervening agents.